Method and apparatus for controlling uplink power in wireless communication system

ABSTRACT

A method and apparatus for controlling an uplink power in a wireless communication system is provided. A user equipment (UE) allocates a first minimum reserved power for a first carrier group and a second minimum reserved power for a second carrier group, and after allocating the first minimum reserved power and the second minimum power, applies a power sharing rule for remaining power, except the first minimum reserved power and the second minimum reserved power, between the first carrier group and the second carrier group.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for controlling an uplink powerin a wireless communication system.

Related Art

Universal mobile telecommunications system (UMTS) is a 3^(rd) generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). A long-term evolution (LTE) of UMTS is under discussion by the3^(rd) generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

To increase the capacity for the users' demand of services, increasingthe bandwidth may be essential, a carrier aggregation (CA) technology orresource aggregation over intra-node carriers or inter-node carriersaiming at obtaining an effect, as if a logically wider band is used, bygrouping a plurality of physically non-continuous bands in a frequencydomain has been developed to effectively use fragmented small bands.Individual unit carriers grouped by carrier aggregation is known as acomponent carrier (CC). For inter-node resource aggregation, for eachnode, carrier group (CG) can be established here one CG can havemultiple CCs. Each CC is defined by a single bandwidth and a centerfrequency.

In LTE Rel-12, a new study on small cell enhancement has started, wheredual connectivity is supported. Dual connectivity is an operation wherea given UE consumes radio resources provided by at least two differentnetwork points (master eNB (MeNB) and secondary eNB (SeNB)) connectedwith non-ideal backhaul while in RRC CONNECTED. Furthermore, each eNBinvolved in dual connectivity for a UE may assume different roles. Thoseroles do not necessarily depend on the eNB's power class and can varyamong UEs.

Uplink power control determines the average power over a single carrierfrequency division multiple access (SC-FDMA) symbol in which thephysical channel is transmitted. Uplink power control controls thetransmit power of the different uplink physical channels. Efficientuplink power control method for CA or dual connectivity may be required.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for controlling anuplink power in a wireless communication system. The present inventionprovides a method for controlling an uplink power when a user equipment(UE) is configured with inter-site carriers over ideal or non-idealbackhaul where independent scheduling and power control is performed ateach site. The present invention provides a method for configuringminimum reserved transmission power for each carrier group, and applyingpower sharing rule for unused transmission power in case that the UEexperiences the limited power due to its maximum allowed power.

In an aspect, a method for controlling, by a user equipment (UE), uplinkpower in a wireless communication system is provide. The method includesallocating a first minimum reserved power for a first carrier group anda second minimum reserved power for a second carrier group, and afterallocating the first minimum reserved power and the second minimumpower, applying a power sharing rule for remaining power, except thefirst minimum reserved power and the second minimum reserved power,between the first carrier group and the second carrier group.

In another aspect, a user equipment (UE) in a wireless communicationsystem is provided. The UE includes a radio frequency (RF) unit fortransmitting or receiving a radio signal, and a processor coupled to theRF unit, and configured to allocate a first minimum reserved power for afirst carrier group and a second minimum reserved power for a secondcarrier group, and after allocating the first minimum reserved power andthe second minimum power, apply a power sharing rule for remainingpower, except the first minimum reserved power and the second minimumreserved power, between the first carrier group and the second carriergroup.

Separate minimum reserved power can be guaranteed for each eNodeB (eNB)or each carrier group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows structure of a radio frame of 3GPP LTE.

FIG. 3 shows a resource grid for one downlink slot.

FIG. 4 shows structure of a downlink subframe.

FIG. 5 shows structure of an uplink subframe.

FIG. 6 shows an example of a carrier aggregation of 3GPP LTE-A.

FIG. 7 shows an example of dual connectivity to a macro cell and a smallcell.

FIG. 8 shows an example of power reduction due to PRACH transmission inpower limited case.

FIG. 9 and FIG. 10 show an example of uplink power allocation accordingto an embodiment of the present invention.

FIG. 11 shows an example of a method for controlling uplink poweraccording to an embodiment of the present invention.

FIG. 12 shows an example of two-step power limit approach according toan embodiment of the present invention.

FIG. 13 shows another example of two-step power limit approach accordingto an embodiment of the present invention.

FIG. 14 shows an example of latency processing of a UE.

FIG. 15 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Techniques, apparatus and systems described herein may be used invarious wireless access technologies such as code division multipleaccess (CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), orthogonal frequency division multiple access(OFDMA), single carrier frequency division multiple access (SC-FDMA),etc. The CDMA may be implemented with a radio technology such asuniversal terrestrial radio access (UTRA) or CDMA2000. The TDMA may beimplemented with a radio technology such as global system for mobilecommunications (GSM)/general packet radio service (GPRS)/enhanced datarates for GSM evolution (EDGE). The OFDMA may be implemented with aradio technology such as institute of electrical and electronicsengineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20,evolved-UTRA (E-UTRA) etc. The UTRA is a part of a universal mobiletelecommunication system (UMTS). 3rd generation partnership project(3GPP) long term evolution (LTE) is a part of an evolved-UMTS (E-UMTS)using the E-UTRA. The 3GPP LTE employs the OFDMA in downlink and employsthe SC-FDMA in uplink. LTE-advance (LTE-A) is an evolution of the 3GPPLTE. For clarity, this application focuses on the 3GPP LTE/LTE-A.However, technical features of the present invention are not limitedthereto.

FIG. 1 shows a wireless communication system. The wireless communicationsystem 10 includes at least one base station (BS) 11. Respective BSs 11provide a communication service to particular geographical areas 15 a,15 b, and 15 c (which are generally called cells). Each cell may bedivided into a plurality of areas (which are called sectors). A userequipment (UE) 12 may be fixed or mobile and may be referred to by othernames such as mobile station (MS), mobile terminal (MT), user terminal(UT), subscriber station (SS), wireless device, personal digitalassistant (PDA), wireless modem, handheld device. The BS 11 generallyrefers to a fixed station that communicates with the UE 12 and may becalled by other names such as evolved-NodeB (eNB), base transceiversystem (BTS), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongsis called a serving cell. A BS providing a communication service to theserving cell is called a serving BS. The wireless communication systemis a cellular system, so a different cell adjacent to the serving cellexists. The different cell adjacent to the serving cell is called aneighbor cell. A BS providing a communication service to the neighborcell is called a neighbor BS. The serving cell and the neighbor cell arerelatively determined based on a UE.

This technique can be used for downlink or uplink. In general, downlinkrefers to communication from the BS 11 to the UE 12, and uplink refersto communication from the UE 12 to the BS 11. In downlink, a transmittermay be part of the BS 11 and a receiver may be part of the UE 12. Inuplink, a transmitter may be part of the UE 12 and a receiver may bepart of the BS 11.

The wireless communication system may be any one of a multiple-inputmultiple-output (MIMO) system, a multiple-input single-output (MISO)system, a single-input single-output (SISO) system, and a single-inputmultiple-output (SIMO) system. The MIMO system uses a plurality oftransmission antennas and a plurality of reception antennas. The MISOsystem uses a plurality of transmission antennas and a single receptionantenna. The SISO system uses a single transmission antenna and a singlereception antenna. The SIMO system uses a single transmission antennaand a plurality of reception antennas. Hereinafter, a transmissionantenna refers to a physical or logical antenna used for transmitting asignal or a stream, and a reception antenna refers to a physical orlogical antenna used for receiving a signal or a stream.

FIG. 2 shows structure of a radio frame of 3GPP LTE. Referring to FIG.2, a radio frame includes 10 subframes. A subframe includes two slots intime domain. A time for transmitting one subframe is defined as atransmission time interval (TTI). For example, one subframe may have alength of 1 millisecond (ms), and one slot may have a length of 0.5 ins.One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in time domain. Since the 3GPP LTE uses theOFDMA in the downlink, the OFDM symbol is for representing one symbolperiod. The OFDM symbols may be called by other names depending on amultiple-access scheme. For example, when SC-FDMA is in use as an uplinkmulti-access scheme, the OFDM symbols may be called SC-FDMA symbols. Aresource block (RB) is a resource allocation unit, and includes aplurality of contiguous subcarriers in one slot. The structure of theradio frame is shown for exemplary purposes only. Thus, the number ofsubframes included in the radio frame or the number of slots included inthe subframe or the number of OFDM symbols included in the slot may bemodified in various manners.

3GPP LTE defines that one slot includes seven OFDM symbols in a normalcyclic prefix (CP) and one slot includes six OFDM symbols in an extendedCP.

The wireless communication system may be divided into a frequencydivision duplex (FDD) scheme and a time division duplex (TDD) scheme.According to the FDD scheme, an uplink transmission and a downlinktransmission are made at different frequency bands. According to the TDDscheme, an uplink transmission and a downlink transmission are madeduring different periods of time at the same frequency band. A channelresponse of the TDD scheme is substantially reciprocal. This means thata downlink channel response and an uplink channel response are almostthe same in a given frequency band. Thus, the TDD-based wirelesscommunication system is advantageous in that the downlink channelresponse can be obtained from the uplink channel response. In the TDDscheme, the entire frequency band is time-divided for uplink anddownlink transmissions, so a downlink transmission by the BS and anuplink transmission by the UE cannot be simultaneously performed. In aTDD system in which an uplink transmission and a downlink transmissionare discriminated in units of subframes, the uplink transmission and thedownlink transmission are performed in different subframes.

FIG. 3 shows a resource grid for one downlink slot. Referring to FIG. 3,a downlink slot includes a plurality of OFDM symbols in time domain. Itis described herein that one downlink slot includes 7 OFDM symbols, andone RB includes 12 subcarriers in frequency domain as an example.However, the present invention is not limited thereto. Each element onthe resource grid is referred to as a resource element (RE). One RBincludes 12×7 resource elements. The number N^(DL) of RBs included inthe downlink slot depends on a downlink transmit bandwidth. Thestructure of an uplink slot may be same as that of the downlink slot.

The number of OFDM symbols and the number of subcarriers may varydepending on the length of a CP, frequency spacing, and the like. Forexample, in case of a normal CP, the number of OFDM symbols is 7, and incase of an extended CP, the number of OFDM symbols is 6. One of 128,256, 512, 1024, 1536, and 2048 may be selectively used as the number ofsubcarriers in one OFDM symbol.

FIG. 4 shows structure of a downlink subframe. Referring to FIG. 4, amaximum of three OFDM symbols located in a front portion of a first slotwithin a subframe correspond to a control region to be assigned with acontrol channel. The remaining OFDM symbols correspond to a data regionto be assigned with a physical downlink shared chancel (PDSCH). Examplesof downlink control channels used in the 3GPP LTE includes a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), a physical hybrid automatic repeat request (HARQ)indicator channel (PHICH), etc. The PCFICH is transmitted at a firstOFDM symbol of a subframe and carries information regarding the numberof OFDM symbols used for transmission of control channels within thesubframe. The PHICH is a response of uplink transmission and carries anHARQ acknowledgment (ACK)/non-acknowledgment (NACK) signal. Controlinformation transmitted through the PDCCH is referred to as downlinkcontrol information (DCI). The DCI includes uplink or downlinkscheduling information or includes an uplink transmit (Tx) power controlcommand for arbitrary UE groups.

The PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, a resource allocation of anupper-layer control message such as a random access response transmittedon the PDSCH, a set of Tx power control commands on individual UEswithin an arbitrary UE group, a Tx power control command, activation ofa voice over IP (VoIP), etc. A plurality of PDCCHs can be transmittedwithin a control region. The UE can monitor the plurality of PDCCHs. ThePDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups.

A format of the PDCCH and the number of bits of the available PDCCH aredetermined according to a correlation between the number of CCEs and thecoding rate provided by the CCEs. The BS determines a PDCCH formataccording to a DCI to be transmitted to the UE, and attaches a cyclicredundancy check (CRC) to control information. The CRC is masked with aunique identifier (referred to as a radio network temporary identifier(RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is fora specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UEmay be masked to the CRC. Alternatively, if the PDCCH is for a pagingmessage, a paging indicator identifier (e.g., paging-RNTI (P-RNTI)) maybe masked to the CRC. If the PDCCH is for system information (morespecifically, a system information block (SIB) to be described below), asystem information identifier and a system information RNTI (SI-RNTI)may be masked to the CRC. To indicate a random access response that is aresponse for transmission of a random access preamble of the UE, arandom access-RNTI (RA-RNTI) may be masked to the CRC.

FIG. 5 shows structure of an uplink subframe. Referring to FIG. 5, anuplink subframe can be divided in a frequency domain into a controlregion and a data region. The control region is allocated with aphysical uplink control channel (PUCCH) for carrying uplink controlinformation. The data region is allocated with a physical uplink sharedchannel (PUSCH) for carrying user data. When indicated by a higherlayer, the UE may support a simultaneous transmission of the PUSCH andthe PUCCH. The PUCCH for one UE is allocated to an RB pair in asubframe. RBs belonging to the RB pair occupy different subcarriers inrespective two slots. This is called that the RB pair allocated to thePUCCH is frequency-hopped in a slot boundary. This is said that the pairof RBs allocated to the PUCCH is frequency-hopped at the slot boundary.The UE can obtain a frequency diversity gain by transmitting uplinkcontrol information through different subcarriers according to time.

Uplink control information transmitted on the PUCCH may include a hybridautomatic repeat request (HARQ) acknowledgement/non-acknowledgement(ACK/NACK), a channel quality indicator (CQI) indicating the state of adownlink channel, a scheduling request (SR), and the like.

The PUSCH is mapped to an uplink shared channel (UL-SCH), a transportchannel. Uplink data transmitted on the PUSCH may be a transport block,a data block for the UL-SCH transmitted during the TTI. The transportblock may be user information. Or, the uplink data may be multiplexeddata. The multiplexed data may be data obtained by multiplexing thetransport block for the UL-SCH and control information. For example,control information multiplexed to data may include a CQI, a precodingmatrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Orthe uplink data may include only control information.

Carrier aggregation (CA) is described. It may be referred to Section 5.5of 3GPP TS 36.300 V11.6.0 (2013-06).

In CA, two or more component carriers (CCs) are aggregated in order tosupport wider transmission bandwidths up to 100 MHz or more. A UE maysimultaneously receive or transmit on one or multiple CCs depending onits capabilities. A UE with single timing advance capability for CA cansimultaneously receive and/or transmit on multiple CCs corresponding tomultiple serving cells sharing the same timing advance (multiple servingcells grouped in one timing advance group (TAG)). A UE with multipletiming advance capability for CA can simultaneously receive and/ortransmit on multiple CCs corresponding to multiple serving cells withdifferent timing advances (multiple serving cells grouped in multipleTAGs). E-UTRAN ensures that each TAG contains at least one serving cell.A non-CA capable UE can receive on a single CC and transmit on a singleCC corresponding to one serving cell only (one serving cell in one TAG).

A serving cell is combination of downlink and optionally uplinkresources. That is, a serving cell may consist of one DL CC and one ULCC. Alternatively, a serving cell may consist of one DL CC. CA may havea plurality of serving cells. The plurality of serving cells may consistof one primary serving cell (PCell) and at least one secondary servingcell (SCell). PUCCH transmission, random access procedure, etc., may beperformed only in the PCell.

FIG. 6 shows an example of a carrier aggregation of 3GPP LTE-A.Referring to FIG. 6, each CC has a bandwidth of 20 MHz, which is abandwidth of 3GPP LTE. Up to 5 CCs or more may be aggregated, so maximumbandwidth of 100 MHz or more may be configured.

CA is supported for both contiguous and non-contiguous CCs with each CClimited to a maximum of 110 RBs in the frequency domain using theRel-8/9 numerology.

It is possible to configure a UE to aggregate a different number of CCsoriginating from the same eNB and of possibly different bandwidths inthe UL and the DL. The number of DL CCs that can be configured dependson the DL aggregation capability of the UE. The number of UL CCs thatcan be configured depends on the UL aggregation capability of the UE. Intypical TDD deployments, the number of CCs and the bandwidth of each CCin UL and DL is the same. A number of TAGs that can be configureddepends on the TAG capability of the UE.

CCs originating from the same eNB need not to provide the same coverage.

CCs shall be LTE Rel-8/9 compatible. Nevertheless, existing mechanisms(e.g., barring) may be used to avoid Rel-8/9 UEs to camp on a CC.

The spacing between center frequencies of contiguously aggregated CCsshall be a multiple of 300 kHz. This is in order to be compatible withthe 100 kHz frequency raster of Rel-8/9 and at the same time preserveorthogonality of the subcarriers with 15 kHz spacing. Depending on theaggregation scenario, the n×300 kHz spacing can be facilitated byinsertion of a low number of unused subcarriers between contiguous CCs.

For TDD CA, the downlink/uplink configuration is identical acrosscomponent carriers in the same band and may be the same or differentacross component carriers in different bands.

Dual connectivity is described.

FIG. 7 shows an example of dual connectivity to a macro cell and a smallcell. Referring to FIG. 7, the UE is connected to both the macro celland the small cell. A macro cell eNB serving the macro cell is the MeNBin dual connectivity, and a small cell eNB serving the small cell is theSeNB in dual connectivity. The MeNB is an eNB which terminates at leastS1-MME and therefore act as mobility anchor towards the CN in dualconnectivity. If a macro eNB exists, the macro eNB may function as theMeNB, generally. The SeNB is an eNB providing additional radio resourcesfor the UE, which is not the MeNB, in dual connectivity. The SeNB may begenerally configured for transmitting best effort (BE) type traffic,while the MeNB may be generally configured for transmitting other typesof traffic such as VoIP, streaming data, or signaling data. Theinterface between the MeNB and SeNB is called Xn interface. The Xninterface is assumed to be non-ideal, i.e., the delay in Xn interfacecould be up to 60 ms.

Uplink power control according to the current specification of 3GPP LTEis described. It may be referred to Section of 5.1 of 3GPP TS 36.213V11.3.0 (2013-06). For PUSCH, the transmit power P̂_(PUSCH,c)(i) is firstscaled by the ratio of the number of antennas ports with a non-zeroPUSCH transmission to the number of configured antenna ports for thetransmission scheme. The resulting scaled power is then split equallyacross the antenna ports on which the non-zero PUSCH is transmitted. ForPUCCH or sounding reference signal (SRS), the transmit powerP̂_(PUCCH)(i) or P̂_(SRS,c)(i) is split equally across the configuredantenna ports for PUCCH or SRS. P̂_(SRS,c)(i) is the linear value ofP_(SRS,c)(i).

Uplink power control for the PUSCH is described. The setting of the UEtransmit power for a PUSCH transmission is defined as follows. If the UEtransmits PUSCH without a simultaneous PUCCH for the serving cell c,then the UE transmit power P_(PUSCH,c)(i) for PUSCH transmission insubframe i for the serving cell c is given by Equation 1.

$\begin{matrix}{{P_{{PUSCH},c}(i)} = {\min {\begin{Bmatrix}{P_{{CMAX},c}(i)} \\\begin{matrix}{{10\; {\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O\_ {PUSCH}},c}(j)} +} \\{{{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} + {f_{c}(i)}}\end{matrix}\end{Bmatrix}\lbrack{dBm}\rbrack}}} & {< {{Equation}\mspace{14mu} 1} >}\end{matrix}$

If the UE transmits PUSCH simultaneous with PUCCH for the serving cellc, then the UE transmit power P_(PUSCH,c)(i) for the PUSCH transmissionin subframe i for the serving cell c is given by Equation 2.

$\begin{matrix}{{P_{{PUSCH},c}(i)} = {\min {\begin{Bmatrix}{{10\mspace{11mu} {\log_{10}\left( {{{\hat{P}}_{{CMAX},c}(i)} - {{\hat{P}}_{PUCCH}(i)}} \right)}},} \\\begin{matrix}{{10\; {\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O\_ {PUSCH}},c}(j)} +} \\{{{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} + {f_{c}(i)}}\end{matrix}\end{Bmatrix}\lbrack{dBm}\rbrack}}} & {< {{Equation}\mspace{14mu} 2} >}\end{matrix}$

If the UE is not transmitting PUSCH for the serving cell c, for theaccumulation of transmit power control (TPC) command received with DCIformat 3/3A for PUSCH, the UE shall assume that the UE transmit powerP_(PUSCH,c)(i) for the PUSCH transmission in subframe i for the servingcell c is computed by Equation 3.

P _(PUSCH,c)(i)=min{P _(CMAX,c)(i),P _(O) _(_) _(PUSCH,c)(1)+α_(c)(1)·PL_(c) +f _(c)(i)} [dBm]  <Equation 3>

In equations described above, P_(CMAX,c)(i) is the configured UEtransmit power in subframe i for serving cell c and P̂_(CMAX,c)(i) is thelinear value of P_(CMAX,c)(i). P̂_(PUCCH)(i) is the linear value ofP_(PUCCH)(i) described below. M_(PUSCH,c)(i) is the bandwidth of thePUSCH resource assignment expressed in number of resource blocks validfor subframe i and serving cell c. P_(O) _(_) _(PUSCH,c)(j) is aparameter composed of the sum of a component P_(O) _(_) _(NOMINAL) _(_)_(PUSCH,c)(j) provided from higher layers for j=0 and 1 and a componentP_(O) _(_) _(UE) _(_) _(PUSCH,c)(j) provided by higher layers for j=0and 1 for serving cell c. PL_(c) is the downlink pathloss estimatecalculated in the UE for serving cell c in dB andPLc=referenceSignalPower−higher layer filtered reference signal receivedpower (RSRP), where referenceSignalPower is provided by higher layersand RSRP and the higher layer filter configuration are defined for thereference serving cell. If serving cell c belongs to a timing advancegroup (TAG) containing the primary cell then, for the uplink of theprimary cell, the primary cell is used as the reference serving cell fordetermining referenceSignalPower and higher layer filtered RSRP. For theuplink of the secondary cell, the serving cell configured by the higherlayer parameter pathlossReferenceLinking is used as the referenceserving cell for determining referenceSignalPower and higher layerfiltered RSRP. If serving cell c belongs to a TAG not containing theprimary cell then serving cell c is used as the reference serving cellfor determining referenceSignalPower and higher layer filtered RSRP.

If the total transmit power of the UE would exceed P̂_(CMAX)(i), the UEscales P̂_(PUSCH,c(i)) for the serving cell c in subframe i such thatEquation 4 is satisfied.

$\begin{matrix}{{\sum\limits_{c}\; {{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}} \leq \left( {{{\hat{P}}_{CMAX}(i)} - {{\hat{P}}_{PUCCH}(i)}} \right)} & {< {{Equation}\mspace{14mu} 4} >}\end{matrix}$

In Equation 4, P̂_(PUSCH)(i) is the linear value of P̂_(PUCCH)(i),P̂_(PUSCH,c)(i) is the linear value of P_(PUSCH,c)(i), P̂_(CMAX)(i) is thelinear value of the UE total configured maximum output power P_(CMAX) insubframe i and w(i) is a scaling factor of P̂_(PUSCH,c)(i) for servingcell c where 0≤w(i)≤1. In case there is no PUCCH transmission insubframe i, P̂_(PUSCH)(i)=0.

If the UE has PUSCH transmission with uplink control information (UCI)on serving cell j and PUSCH without UCI in any of the remaining servingcells, and the total transmit power of the UE would exceed P̂_(CMAX)(i),the UE scales P̂_(PUSCH,c)(i) for the serving cells without UCI insubframe i such that Equation 5 is satisfied.

$\begin{matrix}{{\sum\limits_{c \neq j}\; {{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}} \leq \left( {{{\hat{P}}_{CMAX}(i)} - {{\hat{P}}_{{PUSCH},j}(i)}} \right)} & {< {{Equation}\mspace{14mu} 5} >}\end{matrix}$

P̂_(PUSCH,j)(i) is the PUSCH transmit power for the cell with UCI andw(i) is a scaling factor of P̂_(PUSCH,c)(i) for serving cell c withoutUCI. In this case, no power scaling is applied to P̂_(PUSCH,j)(i) unless

${\sum\limits_{c \neq j}\; {{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}} = 0$

and the total transmit power of the UE still would exceed P̂_(CMAX)(i).Note that w(i) values are the same across serving cells when w(i)>0 butfor certain serving cells w(i) may be zero.

If the UE has simultaneous PUCCH and PUSCH transmission with UCI onserving cell j and PUSCH transmission without UCI in any of theremaining serving cells, and the total transmit power of the UE wouldexceed P̂_(CMAX)(i), the UE obtains P̂_(PUSCH,c)(i) according to Equation6.

$\begin{matrix}{{{\hat{P}}_{{PUSCH},j}(i)} = {{{\min \left( {{{\hat{P}}_{{PUSCH},j}(i)},\left( {{{\hat{P}}_{CMAX}(i)} - {{\hat{P}}_{PUCCH}(i)}} \right)} \right)}{\sum\limits_{c \neq j}\; {{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}}} \leq \left( {{{\hat{P}}_{CMAX}(i)} - {{\hat{P}}_{PUCCH}(i)} - {{\hat{P}}_{{PUSCH},j}(i)}} \right)}} & {< {{Equation}\mspace{14mu} 6} >}\end{matrix}$

If the UE is configured with multiple TAGs, and if the PUCCH/PUSCHtransmission of the UE on subframe i for a given serving cell in a TAGoverlaps some portion of the first symbol of the PUSCH transmission onsubframe i+1 for a different serving cell in another TAG, the UE shalladjust its total transmission power to not exceed P_(CMAX) on anyoverlapped portion.

If the UE is configured with multiple TAGs, and if the PUSCHtransmission of the UE on subframe i for a given serving cell in a TAGoverlaps some portion of the first symbol of the PUCCH transmission onsubframe i+1 for a different serving cell in another TAG, the UE shalladjust its total transmission power to not exceed P_(CMAX) on anyoverlapped portion.

If the UE is configured with multiple TAGs, and if the SRS transmissionof the UE in a symbol on subframe i for a given serving cell in a TAGoverlaps with the PUCCH/PUSCH transmission on subframe i or subframe i+1for a different serving cell in the same or another TAG, the UE shalldrop SRS if its total transmission power exceeds P_(CMAX) on anyoverlapped portion of the symbol.

If the UE is configured with multiple TAGs and more than 2 servingcells, and if the SRS transmission of the UE in a symbol on subframe ifor a given serving cell overlaps with the SRS transmission on subframei for a different serving cell(s) and with PUSCH/PUCCH transmission onsubframe i or subframe i+1 for another serving cell(s), the UE shalldrop the SRS transmissions if the total transmission power exceedsP_(CMAX) on any overlapped portion of the symbol.

If the UE is configured with multiple TAGs, the UE shall, when requestedby higher layers, to transmit physical random access channel (PRACH) ina secondary serving cell in parallel with SRS transmission in a symbolon a subframe of a different serving cell belonging to a different TAG,drop SRS if the total transmission power exceeds P_(CMAX) on anyoverlapped portion in the symbol.

If the UE is configured with multiple TAGs, the UE shall, when requestedby higher layers, to transmit PRACH in a secondary serving cell inparallel with PUSCH/PUCCH in a different serving cell belonging to adifferent TAG, adjust the transmission power of PUSCH/PUCCH so that itstotal transmission power does not exceed P_(CMAX) on the overlappedportion.

Uplink power control for the PUCCH is described. If serving cell c isthe primary cell, the setting of the UE transmit power P_(PUCCH) for thePUCCH transmission in subframe i is defined by Equation 7.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min {\begin{Bmatrix}{{P_{{CMAX},c}(i)},} \\\begin{matrix}{P_{0{\_ {PUCCH}}} + {PL}_{c} + {h\left( {n_{CQI},n_{HARQ},n_{SR}} \right)} +} \\{{\Delta_{F\_ {PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g(i)}}\end{matrix}\end{Bmatrix}\lbrack{dBm}\rbrack}}} & {< {{Equation}\mspace{14mu} 7} >}\end{matrix}$

If the UE is not transmitting PUCCH for the primary cell, for theaccumulation of TPC command received with DCI format 3/3A for PUCCH, theUE shall assume that the UE transmit power P_(PUCCH) for the PUCCHtransmission in subframe i is computed by Equation 8.

P _(PUCCH)(i)=min{P _(CMAX,c)(i),P _(CMAX,c)(i),P ₀ _(_) _(PUCCH) +PL_(c) +g(i)} [dBm]  <Equation 8>

In equations described above, P_(CMAX,c)(i) is the configured UEtransmit power in subframe i for serving cell c. The parameter Δ_(F)_(_) _(PUCCH)(F) is provided by higher layers. If the UE is configuredby higher layers to transmit PUCCH on two antenna ports, the value ofΔ_(TxD)(F′) is provided by higher layers. Otherwise, Δ_(TxD)(F′)=0.h(n_(CQI), n_(HARQ), n_(SR)) is a PUCCH format dependent value, wheren_(CQI) corresponds to the number of information bits for the channelquality information (CQI). n_(SR)=1 if subframe i is configured for SRfor the UE not having any associated transport block for UL-SCH,otherwise n_(SR)=0=0. P_(O) _(_) _(PUCCH) is a parameter composed of thesum of a parameter P_(O) _(_) _(NOMINAL) _(_) _(PUCCH) provided byhigher layers and a parameter P_(O) _(_) _(UE) _(_) _(PUCCH) provided byhigher layers.

Hereinafter, a method for controlling uplink power according toembodiments of the present invention is described. An embodiment of thepresent invention may propose power control aspects when inter-sitecarrier aggregation is used for a UE. Inter-site carrier aggregation maybe defined as that a UE is configured with multiple carriers where atleast two carriers are associated with separate eNBs which may beconnected by ideal backhaul or non-ideal backhaul. when a UE can performsimultaneous two UL transmissions (including PUSCH/PUCCH), the followingcases may be considered.

-   -   Case 1: FDD+FDD or same DL/UL configuration TDD+TDD over idea        backhaul    -   Case 2: FDD+FDD or same DL/UL configuration TDD+TDD over        non-idea backhaul    -   Case 3: FDD+TDD or different DL/UL configuration TDD+TDD over        ideal backhaul    -   Case 4: FDD+TDD or different DL/UL configuration TDD+TDD over        non-ideal backhaul

When a UE cannot be able to perform simultaneous two UL transmissions,the following cases may be considered.

-   -   Case 5: FDD+FDD or same DL/UL configuration TDD+TDD over idea        backhaul    -   Case 6: FDD+FDD or same DL/UL configuration TDD+TDD over        non-idea backhaul    -   Case 7: FDD+TDD or different DL/UL configuration TDD+TDD over        ideal backhaul    -   Case 8: FDD+TDD or different DL/UL configuration TDD+TDD over        non-ideal backhaul

An embodiment of the present invention may focus on a case where powercontrol for each eNB is managed separately. If more than one CC isconfigured within one eNB, uplink power control used in 3GPP LTE rel-11may be applicable among intra-eNB carriers. More specifically, anembodiment of the present invention may consider a case where eachcarrier group is assigned with maximum power which can be used within acarrier group when power limited case (i.e., the sum of required powerfor all uplink channels exceeds the maximum power for the UE) occurs.Furthermore, an embodiment of the present invention may propose how toutilize the total UE power when the total power of requested power percarrier group may exceed the total UE power. Also, an embodiment of thepresent invention may propose how to utilize the minimum reserved powerper carrier group and how to share the unallocated remaining powerbetween carrier groups. Also, an embodiment of the present invention maypropose how to handle power allocation per physical channel such asPRACH and PUCCH. Above description which the embodiments of the presentinvention proposes may be also applied to cases, such as case 1 or case3 described above, where single eNB maintains more than one carriergroup. When a UE is configured with two carrier groups being configuredby a single eNB, the present invention may be applied differently, e.g.,including different parameters. In other words, the present inventionmay be applied to carrier groups configured by a single eNB with someclarifications and changes if necessary.

Hereinafter, for the convenience, a case where more than one carriergroup is configured by a single eNB where each carrier group may have acarrier receiving PUCCH is called “PUCCH offloading”. Each carrier groupmay have multiple carriers, even though the number of PUCCH carrier maybe limited to only one per carrier group.

Further, when power is allocated per carrier group or per eNB, and whenone carrier group is removed due to e.g., radio link failure (RLF) orpoor performance, it may be assumed that parameter becomes invalid evenwithout reconfiguration. For example, it is assumed that minimumguaranteed power is allocated to MeNB and SeNB as 20% and 20%respectively. When the SeNB is de-configured due to RLF, until the SeNBis reconfigured, the power allocation is not used by the UE (thus,reserve power for the SeNB would not be occurred). In other words, powerallocation per carrier group or per eNB may be valid only if two carriergroups or two cNBs are active. Otherwise, the UE shall ignore thoseparameters. This may be interpreted as if a UE is “reconfigured” withdifferent power allocation when a carrier group changes or the SeNBchanges (e.g., assign 100% to the MeNB or the first carrier group withPCell).

1. A method for allocating P_(CMAX), which is configured maximum power,per eNB or per carrier group according to an embodiment of the presentinvention is described. According to this method, P_(CMAX) for each eNBor each carrier group may be configured semi-statically.

According to an embodiment of the present invention, when more than oneeNBs serve a UE, the maximum usable power may be configured by each cNBseparately or separately for each eNB. Or, the maximum usable power maybe configured separately to the carrier group where a PCell belongs andto the group(s) where a super SCell (or, master SCell) belongs. In otherwords, separate maximum power is maintained for each eNB or each carriergroup. Hereinafter, the maximum usable power per each eNB or eachcarrier group according to an embodiment of the present invention isrepresented as P_(CMAX,eNBj), while the maximum power for the UE isrepresented as P_(CMAX). For example, assuming two eNBs, i.e., eNB1 andeNB2, are serving the UE, each eNB may configure different maximumusable power depending on its condition and other factors.Alternatively, only maximum usable power for the second carrier group(e.g., eNB2) may be allocated by the eNB1, and all the remaining power(P_(CMAX)—the maximum power allocated to the second carrier group (orothers)) may be utilized for the first carrier group. Alternatively,only maximum usable power for the first carrier group (e.g., eNB1) maybe allocated by the eNB1, and all the remaining power may be utilizedfor the second carrier group.

Hereinafter, maximum power for the first carrier group (or, first eNB)and maximum power for the second carrier group (or, second eNB) may becalled P_(CMAX,eNB1) and P_(CMAX,eNB2), respectively.P_(CMAX,cNB1)≤P_(CMAX) and P_(CMAX,eNB2)≤P_(CMAX). Depending on itsconfiguration with consideration of maximum power reduction (MPR), theUE may calculate P_(CMAX,eNB1) and P_(CMAX,eNB2) accordingly and reportthe calculated maximum power to two eNBs. To avoid unnecessarycross-carrier-group power scaling issue, the sum of maximum power forboth eNBs may not exceed P_(CMAX) That is,P_(CMAX)=P_(CMAX,eNB1)+P_(CMAX,eNB2). To ensure this, it may beconsidered that the UE will be configured with only one maximum power,i.e., one of either P_(CMAX,eNB1) or P_(CMAX,eNB2), and the othermaximum power will be computed based on the maximum power for the UE.

Alternatively, even if a UE is configured with maximum power for botheNBs, if the sum of maximum power for both eNBs exceeds P_(CMAX), theproper power scaling on the other eNB based on one eNB may beconsidered. More specifically, the power scaling may be applied only ifthe UE experiences power limited case. For example, ifP_(CMAX,eNB1)+P_(CMAX,eNB2)>P_(CMAX), the UE may take one of eitherP_(CMAX,eNB1) or P_(CMAX,eNB2) and the remaining maximum power isadjusted based on min {P_(CMAX)−P_(CMAX,eNB1), P_(CMAX,eNB2)}. In termsof taking which eNB power as intact may be configured. Or, MeNB may bealways maintained or SeNB may be always maintained. In this case, the UEmay indicate the situation to the MeNB such that the MeNB mayreconfigure the maximum usable power for each eNB or each carrier group.If the MeNB allocates only P_(CMAX,eNB2), then the UE may assume thatP_(CMAX,eNB1)=P_(CMAX)−P_(CMAX,eNB2) and reports P_(CMAX,eNB1) to theMeNB.

When each carrier group has multiple carriers configured, maximum powerallocated for each carrier may be smaller than the maximum powerallocated to the entire carrier group. Otherwise, the UE may assume thatthe minimum of two values as the maximum power per carrier. Theseparameters may be used for any uplink transmission to the target eNB.For example, any uplink transmissions to the eNB1 may use P_(CMAX,eNB1)as the maximum power for the eNB1 and any uplink transmissions to theeNB2 may use P_(CMAX,eNB2) as the maximum power for the eNB2. If eacheNB configures multiple CCs, power control within an eNB may beperformed following uplink power control used in 3GPP LTE rel-11.Alternatively, P_(CMAX,eNB1) and P_(CMAX,eNB2) may be signaled to theeNBs separately. Or, the percentage between two eNBs may also beconfigured where a UE divide the maximum power for the UE to each eNBbased on the configured ratio. For example, if the configured ratio is80%/20% between two eNBs, 80% of the configured maximum power for the UEmay be used for transmission to the eNB1, whereas 20% of the maximumpower for the UE may be used for transmission to the eNB2, respectively.

P_(CMAX,eNB1) and P_(CMAX,eNB2) may be exchanged between two eNBs. TheMeNB may inform the information to the SeNB implicitly or explicitly.When a UE is configured with the values, the UE may implicitly informthe SeNB.

Individual power control for each channel/signal in each carriergroup/eNB may follow uplink power control used in 3GPP LTE rel-11. Whenpower for each signal is determined, for CCs belonging to the same eNB,power scaling may be performed as follows. The detailed function may notbe limited to the description below. However, in principle, powercontrol may be performed separately for each eNB (e.g., MeNB/SeNB orstand-alone eNB/assisting eNB), and uplink power control used in 3GPPLTE rel-11 may be applied within each power control loop.

If P̂_(CMAX,eNBj)(i) is configured for eNBj, and if the total transmitpower of the UE would exceed P̂_(CMAX,eNB)j(i), the UE scalesP̂_(PUSCH,eNBj,c)(i) for the serving cell c belonging to eNBj in subframei such that Equation 9 is satisfied.

$\begin{matrix}{{\sum\limits_{c}\; {{w(i)} \cdot {{\hat{P}}_{{PUSCH},{eNBj},c}(i)}}} \leq \left( {{{\hat{P}}_{{CMAX},{eNBj}}(i)} - {{\hat{P}}_{{PUCCH},{eNBj}}(i)}} \right)} & {< {{Equation}\mspace{14mu} 9} >}\end{matrix}$

In Equation 9, P̂_(PUCCH,enBj)(i) is the linear value ofP_(PUCCH,eNBj)(i), P̂_(PUSCH,eNBj,c)(i) is the linear value ofP_(PUSCH,eNBj,c)(i), P̂_(CMAX,eNBj)(i) is the linear value of the UEtotal configured maximum output power P_(CMAX,eNBj) and w(i) is ascaling factor of P̂_(PUSCH,eNBj,c)(i) for serving cell c where 0≤w(i)≤1.In case there is no PUCCH transmission in subframe i,P̂_(PUCCH,eNBj)(i)=0.

Otherwise, if P̂_(CMAX,eNB1-j)(i) is configured for eNB_(1-j), thenP̂_(CMAX,eNBj)(i)=P_(CMAX)−P̂_(CMAX,eNB1-j)(i). If the total transmitpower of the UE would exceed P̂_(CMAX,eNB)j(i), the UE scalesP̂_(PUSCH,eNBj,c)(i) for the serving cell c belonging to eNBj in subframei such that Equation 9 described above is satisfied.

In other words, power control may be handled separately per eNB (permedia access control (MAC)) where multiple CCs and power scaling withinan eNB may be handled same as 3GPP LTE rel-11 carrier aggregation aslong as PUCCH is transmitted on only one CC (PCell or PCell-equivalentCC).

Further, inter-eNB power control may be also necessary. Equation 10shows total power of each eNBj.

$\begin{matrix}{{{TP}_{{sum},{eNBj}}(i)} = {{\sum\limits_{c}\; {{w(i)} \cdot {{\hat{P}}_{{PUSCH},{eNBj},c}(i)}}} + {{\hat{P}}_{{PUCCH},{eNBj}}(i)}}} & {< {{Equation}\mspace{14mu} 10} >}\end{matrix}$

As a first condition for inter-eNB power control, offset between totalpowers may be considered. The first condition for inter-eNB powercontrol may be omitted depending on band combination. If uplink bandsare not close each other, the first condition may not be addressed.Specifically, for intra-band dual connectivity, if Equation 11 issatisfied, it may be considered that the first condition is passed.

|TP _(sum,eNB0)(i)−TP _(sum,eNB1)(i)|<=P _(threshold)  <Equation 11>

In Equation 11, P_(threshold) may either signaled by higher layer orcalculated based on band-combinations of aggregated carriers as well asaggregated eNBs. Otherwise, power scaling may be applied again accordingto Equation 12.

$\begin{matrix}{{{\sum\limits_{c}\; {{w(i)} \cdot {{\hat{P}}_{{PUSCH},{{eNB}0},c}(i)}}} \leq \left( {{{TEMP}_{{CMAX},{{eNB}\; 0}}(i)} - {{\hat{P}}_{{PUCCH},{{eNB}\; 0}}(i)}} \right)}\mspace{20mu} {{{TEMP}_{{CMAX},{{eNB}\; 0}}(i)} = {P_{treshold} + {{TP}_{{sum},{{eNB}\; 1}}(i)}}}} & {< {{Equation}\mspace{14mu} 12} >}\end{matrix}$

In Equation 12, it is assumed that eNB0 is the MeNB (or higher power ULtransmission target eNB). Alternatively, when first condition fails, theUE may drop uplink signals according to the priority list.

As a second condition for inter-eNB power control, sum of two powers maybe considered. If total power for two eNBs exceeds P_(CMAX), uplinksignals may be dropped according to the priority. Or, scaling may beperformed as well. The first/second condition may not be needed when aUE cannot be able to perform simultaneous two UL transmissions.

2. A method for allocating P_(alloc), which is configured minimumreserved power, per eNB or per carrier group according to an embodimentof the present invention is described.

According to an embodiment of the present invention, when more than oneeNBs serve a UE, P_(alloc) may be configured by each eNB separately orseparately for each eNB. Or, P_(alloc) may be configured separately tothe carrier group where PCell belongs and to the group(s) where a superSCell (or master SCell) belongs. P_(alloc) may be used to guaranteeminimum reserved power allocation per carrier group or per eNB whenpower limited case occurs. In other words, separate minimum reservedpower is maintained for each eNB or each carrier group. These parametersmay be used along with the maximum usable power per eNB or otherparameters such as P_(CMAX,c) as well.

Various methods for allocating P_(alloc) per each carrier group or pereach eNB may be considered as follows.

(1) The MeNB may configure both P_(alloc,eNB1) and P_(alloc,eNB2)respectively. That is, the MeNB may determine the minimum reserved powerallocated to each eNB when there is at least one uplink transmission.

(2) P_(alloc) may be inferred from the maximum usable power per eNB. Forexample, P_(alloc) for the SeNB may be calculated asP_(CMAX)−P_(CMAX,MeNB) (similarly to P_(alloc) for the MeNB) if themaximum usable power per eNB is configured. In this case, regardless ofpower limited case, each eNB may utilize the power up to P_(CMAX,eNB)only and P_(CMAX)−P_(CMAX,eNB) may be reserved for the successivesubframe transmission from the other eNB.

(3) The MeNB and SeNB may configure independently P_(alloc) per eNB. AUE may report “mis-configuration” if the summation of two values exceedthe maximum power for the UE. Alternatively, if the sum exceeds themaximum power for the UE, the UE may calculateP_(alloc,SeNB)=P_(CMAX)−P_(alloc,MeNB) (set to the remaining power) sothat it would not exceed the maximum power for the UE. Or,P_(alloc,MeNB)=P_(CMAX)−P_(alloc,SeNB) may be also considerable. Or, itmay be further considerable that the network may configure which one toreduce the power between two eNBs. Furthermore, it may be also notablethat the minimum reserved power for each carrier group or each eNB maybe configured as a form of ratio instead of absolute values. The ratiomay be applied based on the UE configured maximum power after applyingnecessary MPR and other reductions. Alternatively, the ratio may beapplied based on the maximum power for the UE per power class (such as23 dBm) if the summation of two values do not exceed P_(CMAX). However,the ratio may be applied based on P_(CMAX) once the summation of twovalues by ratio computation exceeds P_(CMAX). For example, if there is 6dB power loss due to MPR, and ratio is 50%/50%, the UE may apply theratio based on P_(CMAX). Another approach of applying P_(alloc,xeNB) isto P apply MPR and everything by setting P_(alloc,xeNB) as the maximumpower per each carrier group. The techniques described here may also beapplicable to P_(CMAX,xeNB) as well described above.

(4) The UE may determine P_(alloc) per eNB and report the values to botheNBs. The UE may calculate P_(alloc) for both eNBs based on pathloss andsome higher layer configured power control parameters.

(5) The MeNB may configure only P_(alloc,eNB2) (for the SeNB) which theUE may use as a minimum reserved power for SeNB transmission. When powerlimited case occurs, (optionally if the UE has at least one uplinktransmission to the SeNB), the minimum reserved power for the SeNBshould be guaranteed. In this case, if the McNB wants to configure allpower to the McNB, the configured P_(alloc,eNB2) value may be zero. Themotivation of allocating P_(alloc,eNB2) to the SeNB is to guarantee aminimum reserved power to the SeNB when power limited case occurs.P_(alloc,eNB2) may be used as a baseline power for the SeNB such that atleast P_(alloc,eNB2) power is used toward the SeNB when the requiredpower towards the SeNB exceeds P_(alloc,eNB2) if the power limited caseoccurs.

Once P_(alloc) is configured, P_(alloc) may be utilized according tovarious methods described as follows. For example, if P_(alloc) per eNBis configured for both the MeNB and SeNB respectively, the minimumreserved power for each carrier group or each eNB may be set as theconfigured P_(alloc) For unused power(=P_(CMAX)−P_(alloc,eNB1)−P_(alloc,eNB2)), power sharing rule may beapplied. If either carrier group requires less power than the minimumreserved power, the remaining power may be used by the other carriergroup. For another example, if P_(alloc) per eNB is configured for theSeNB only, the minimum reserved power for the SeNB may be set as theconfigured P_(alloc,SeNB). For unused power (=P_(CMAX)−P_(alloc,SeNB)),power sharing rule may be applied. The similar procedure may beapplicable to the case where P_(alloc) is configured only for the MeNB.For another example, at subframe n for the MeNB, and subframe k for theSeNB, assume that subframe n for the MeNB is overlapped with subframe kand k+1 for the SeNB. If at least one subframe has uplink transmissioneither in subframe k or subframe k+1 for the SeNB, uplink power for theMeNB should not exceed P_(CMAX)−P_(alloc,SeNB). In other words, for theSeNB transmission, minimum reserved power should be reserved. This maybe generalized to the case where a UE should not allocate more thanP_(CMAX)−P_(alloc,SeNB) towards MeNB transmission if at least onesubframe is uplink subframe per configuration (either subframe k orsubframe k+1 for the SeNB). The similar condition may be applicable tothe MeNB as well. For unused power, power sharing rule may be applied.After applying power sharing rule, power scaling used incarrier-aggregation framework may be performed within a group.

Applying power sharing rule is described. All unused power may be firstassigned to the MeNB, and then the remaining power not allocated to theMeNB may be assigned to the SeNB if exists. Alternatively, all unusedpower may be assigned to the PCell, and then the remaining power may beassigned to the sPCell (special scell in secondary carrier group (SCG)).The remaining power may be equally or weighted equally assigned to theMeNB and SeNB if exists. Alternatively, all unused power may be assignedequally to MeNB/SeNB. Alternatively, all unused power may be assignedwith weight for MeNB/SeNB (e.g., 80%/20%). Alternatively, all unusedpower may be assigned according to channel/UCI type priority betweenMeNB/SeNB (such asPRACH≥PUCCH+SR≥PUCCH+HARQ-ACK≥PUCCH+CSI≥PUSCH+HARQ-ACK≥PUSCH+CSI≥PUSCH,etc).

Channel priority between two carrier groups (or, two eNBs) is furtherdescribed in detail. Unused power may be allocated depending on powersharing rule between two carrier groups. In the following some examplesare described.

-   -   PRACH on MeNB/PRACH on SeNB:PRACH on the MeNB or PCell may be        always be prioritized. P_(alloc) per eNB may not limit the power        for PRACH. In other words, PRACH transmission to the SeNB may        use the unused power after PRACH transmission to the MeNB        regardless of configuration of P_(alloc). If PRACH on the SeNB        cannot be allocated with the required power, PRACH may be        delayed or dropped. Other channels in the MeNB or SeNB (e.g.,        other than PUCCH or PRACH) may be dropped if the UE experiences        power limited case. For PUCCH or PRACH, the remaining power may        be still applied (and thus power-scaled) and transmitted.    -   PRACH on MeNB/PUCCH on SeNB:PRACH on the MeNB may always be        prioritized. P_(alloc) per eNB may not limit the power for        PRACH. In other words, PUCCH transmission to the SeNB may use        the unused power after PRACH transmission to the MeNB. Other        channels in the MeNB or SeNB (other than PUCCH or PRACH) may be        dropped if the UE experiences power limited case. Alternatively,        PRACH on the SeNB may have higher priority than PUCCH such that        the required power can be allocated regardless of the        configuration of minimum reserved power.    -   PUCCH on MeNB/PRACH on SeNB:PRACH transmission to the SeNB may        use (P_(CMAX)−P_(PUCCH)) where P_(PUCCH)=min (PUCCH power,        P_(alloc,MeNB)). In other words, PRACH transmission to the SeNB        may use the unused power after PUCCH transmission to the MeNB.        Other channels in the MeNB or SeNB (other than PUCCH or PRACH)        may be dropped if the UE experiences power limited case.    -   PUCCH on MeNB/PUCCH on SeNB: P_(alloc) per eNB may be used for        splitting power between two PUCCH transmissions. Moreover, when        P_(CMAX,eNB) is allocated, the maximum usable power per eNB may        be used to determine the power for PUCCH transmission. The same        thing may be applied to the case of PUCCH or PUSCH with HARQ-ACK        on MeNB/PUCCH or PUSCH with HARQ-ACK on SeNB. The power for the        PUCCH (or PUSCH with UCI) may be determined as min (PUCCH power,        P_(alloc,eNB)). In other words, if both uplink transmission has        HARQ-ACK transmission, the allocated power may be used to        determine power for HARQ-ACK transmission. If there is unused        power left and some other uplink channels exists (such as        PUSCH), the unused power may be used for transmission of other        channels. This may be generalized to cases where PUSCH with UCI        has the same priority to the PUCCH. Moreover, PUCCH without        HARQ-ACK may be treated as “non-PUCCH” or non-HARQ ACK, and thus        may not assign the P_(alloc) in that case depending on the        available power.    -   PUSCH on MeNB/PUCCH on SeNB: Priority may be given to the PUCCH        on the SeNB and the power for the PUCCH may be assigned as min        (PUCCH power, P_(alloc,SeNB)) Unused power may be allocated to        the PUSCH transmission of the MeNB.    -   PUCCH on MeNB/PUSCH on SeNB: similarly, the PUCCH on the MeNB        may be maintained. In this case, if P_(alloc) for the MeNB is        configured as well, the power for the PUCCH on the MeNB is        determined as min (PUCCH power, P_(alloc,MeNB)). Unused power        may be used for other transmissions.    -   PUCCH/PUSCH on MeNB/PUCCH on SeNB: minimum reserved power        P_(alloc) is used for PUCCH transmission for each eNB. The PUSCH        on the MeNB may be allocated from unused power. Thus, power for        the PUCCH on the MeNB=min (PUCCH power, P_(alloc,MeNB)), and        power for the PUCCH on the SeNB=min (PUCCH power,        P_(alloc,ScNB)). When unused power is allocated to PUSCH        transmissions, it may be equally or weighted distributed across        eNBs or the MeNB may utilize all the unused power.    -   PUSCH on MeNB/PUSCH on MeNB: Equal power scaling may be        utilized. Or weighted scaling may be utilized. In this case,        PUSCH with UCI may have higher priority over PUSCH without UCI.

Once P_(alloc,xeNB) is configured, it may be applicable to the PUCCH andPUSCH. However, the power allocated to PRACH and SRS may be treatedseparately.

In the description above, the PUCCH generally refers the PUCCH withHARQ-ACK, PUSCH with HARQ-ACK (and may be PUCCH with UCI and PUSCH withUCI). Power of SRS may not be assured by P_(alloc) per eNB ifconfigured. In other words, if only SRS transmission is scheduled toanother eNB in power limited case, the SRS may be dropped regardless ofP_(alloc) configuration. P_(alloc) may also be applicable to PRACHtransmission as well similar to PUCCH transmission. In other words, whenPRACH/PRACH transmission occurs, P_(alloc) per eNB may be used for powerfor the PRACH. P_(CMAX,eNB) may be used instead of P_(alloc, eNB) in theabove prioritization and power allocation, if P_(CMAX,eNB) isconfigured. For example, P_(CMAX,eNB) may be used only when PUCCH/PUCCHcollide or PRACH/PRACH collide.

Further, the PRACH may utilize the maximum power for the UE regardlessof power split between two eNBs. More specifically, PRACH transmissionof master carrier group (MCG) may be able to utilize the maximum powerfor the UE. If on-going transmission and PRACH transmission collide witheach other, the UE may reduce power for the on-going transmission if sumof power for the on-going transmission and power for the PRACHtransmission exceeds the maximum power for the UE. Power for otherchannel (such as PUSCH or PUCCH) on on-going transmission may bepower-scaled at least in the overlapped portion between PRACHtransmission and on-going transmission.

FIG. 8 shows an example of power reduction due to PRACH transmission inpower limited case. Referring to FIG. 8, maximum power in subframe k isconfigured as Pmax (n, k) and maximum power in subframe (k+1) isconfigured as Pmax (n, k+1). In the middle of uplink transmission insubframe k, PRACH transmission is performed. Since the sum of requiredpower for the PRACH transmission (P1) and power for on-goingtransmission (C1, k) exceeds Pmax (n,k), power reduction is performedfor the on-going transmission.

Further, the techniques for P_(alloc) described above may be applicableto the cases where only P_(CMAX,SeNB) is configured. In that case,P_(CMAX,SeNB) may be assumed to be the same as P_(alloc,SeNB).

Further, P_(alloc,eNB) may be represent as “the assured power value”where at least one eNB has higher priority than the other eNB in thosepower range. For example, with 23 dBm power class, a UE may be allowedto have higher priority to the SeNB up to 20 dBm if P_(alloc,SeNB)=20dBm is configured. Similar assumption may be applied to the MeNB aswell. The unused power may be allocated across two eNBs following powersharing rule described above.

FIG. 9 and FIG. 10 show an example of uplink power allocation accordingto an embodiment of the present invention. Subframe #2/#3 and #6/#7 ofeNB1 is used for uplink transmission. Power may be shared between twoeNBs wherever subframes of two eNBs overlap. For example, in subframe#2/#3 in FIG. 10, eNB0 may be prioritized or the unused power may beallocated to eNB0 (e.g., MeNB) as eNB1 does not have any other uplinktransmission. On the other hand, in subframe #6/#7 in FIG. 11, unusedpower may be allocated to eNB1. Actual power allocation may bedetermined based on the power sharing rule between two eNBs or acrossthe channels.

To protect potential uplink transmission in the next subframe in whichthe UE may not know the exact power when determining the currentsubframe's power, the UE may assume that at least minimum reserved poweris allocated to the next subframe including “flexible uplink subframeconfigured by enhanced interference mitigation & traffic adaptation(eIMTA)”. For example, if subframe #3 of eNB1 is used for uplinksubframe, when determining power for subframe #2 of eNB1, it shallconsider minimum reserved power (P_(alloc, eNFB1)) is allocated tosubframe #3 of eNB1 regardless of uplink transmission scheduling orPUCCH scheduling. If no uplink transmission occurs in subframe #3 ofeNB1, the allocated power may be unused. However, it will avoid the casewhere previous transmission may affect the next potential uplinktransmission between two eNBs. In other words, the UE may allocatemaximum power P_(CMAX) to eNB0 only when there is no uplink transmissionscheduled or potentially planned for the overlapped subframes of eNB1(and vice versa). Otherwise, the UE may allocate maximum power of(P_(CMAX)−P_(alloc,eNB1)) to eNB0 to leave the minimum reserved powerfor eNB1. In terms of sharing the unused power between two eNBs, one orsets of alternatives may be used. When there is no uplink scheduled inthe other eNB, the maximum power for the UE may be allocated to one eNBin both overlapped subframes.

More specifically, this may be applied only when asynchronous powercontrol is configured (i.e., a UE is higher layer configured withasynchronous power control mode) or a UE is configured with P_(alloc)value at least one eNB. When multiple TA technique is used, instead oflooking at both overlapped subframes, the UE may only look at onesubframe where the overlap portion is greater than the other. Forexample, the overlap between subframe n and subframe k (between twoeNBs) is 0.8 ms whereas the overlap between subframe n+1 and subframe kis 0.2 ms, the UE may look at only subframe n/k overlap to determineunused power, power scaling and the power limited case. This may beallowed only if the UE is configured with synchronous power control modeor the UE is not capable of shorter processing time or the UE isconfigured by higher layer to perform this way.

For power scaling and dropping for inter-site CA between two eNBs,various methods may be used as follows.

-   -   Power for the PUCCH may not be scaled. When power scaling is        used, the PUCCH has the top priority (other than PRACH), thus        power scaling on the PUCCH should not be attempted. When PUCCHs        are transmitted to different eNBs, PUCCH for PCell eNB may have        higher priority and PUCCH having the lower priority may be        dropped if only PUCCH transmissions are attempted and the total        power for PUCCH transmissions exceeds the maximum power for the        UE. Or, the UE may be configured with priority between two eNBs        to drop PUCCH for PUCCH transmissions with power limited case.    -   PUSCH with UCI has higher priority than PUSCH without UCI    -   Power for the SRS power may not be scaled. If the SRS collides        with other uplink signals, the SRS may be dropped.    -   The PRACH has higher priority than other signals. More than one        PRACH may not be transmitted within a same eNB or a carrier        group. A carrier group may refer to a group contains one carrier        where the PUCCH is transmitted. When PRACHs transmissions to        different eNBs collide with each other, PRACH of PCell eNB has        higher priority. Or, the UE may be configured with priority        between two eNBs. PRACH having lower priority may be dropped.        Power for the PRACH may not be scaled. When the PRACH and PUCCH        collide with each other and power for the PRACH and PUCCH        exceeds the maximum power for the UE, the PUCCH may be dropped.        Alternatively, PUCCH to PCell with PRACH to SCell may be        transmitted with power scaling on the PUCCH.

Generally, PUCCH or PRACH has higher priority than other channels. Thelowest priority would be the SRS compared to other uplink channels andif power limitation occurs, the SRS may be dropped from any CC. If thereis still power limitation issue after dropping the SRS, power scaling onthe PUSCH may be attempted. Even still, there is power limitationbetween PUCCH/PRACH, PUCCH/PUCCH, PRACH/PRACH, and some priority rulemay be needed. Between the PUCCH and PRACH, the PRACH initiated by PDCCHorder has higher priority than the PUCCH. The PUCCH may have higherpriority than other PRACH transmissions.

When PUCCH/PUCCH collides, if duplex modes of two carriers are the same(or two eNBs's PCell), the PCell has higher priority than the superSCell, thus, power scaling on the PUCCH to the SCell may be attempted.The same thing may be applied to PRACH (where detail scaling may befurther different depending on how PRACH is initiated). However, ifduplex modes of two carriers are different from each other, due to thelower number of uplink subframes and thus potentially higher number ofACK/NACK bits transmitted in one uplink PUCCH transmission, the superSCell with TDD may have higher priority than the FDD PCell. When thePCell and super SCell have both TDD configured, TDD DL/UL configurationwith lower number of uplink subframes may have higher priority insteadof putting higher priority on the PCell. Similar scaling rule may beapplied to PRACH/PRACH collision as well.

Alternatively, a UE can be configured to drop uplink signal when totalpower exceeds the maximum power for the UE between two eNBs ULtransmissions. Within one eNB, dropping rule used in 3GPP LTE rel-11 maybe applied. New dropping rule applies only to the cases where inter-siteCA is applied or PUCCH is transmitted to more than one CC within an eNB.Alternatively, when power limited case occurs, then the UE may beconfigured with maximum tolerance per each carrier group which may beused for power scaling/reduction per carrier group. The UE performspower scaling per carrier group by reducing the maximum tolerance level.After power reduction per each carrier group, if the total power stillexceeds the maximum power for the UE, the UE may prioritize transmissionto the MeNB (or C-Plane). Otherwise, unused power may be allocated hackto the MeNB or equally or weighted equally to carrier groups.

Alternatively, the UE may be configured with maximum tolerance for theSeNB. When power limited case occurs, power reduction on the SeNBtransmission is attempted for maximum tolerance level (e.g., 20%tolerance level, SeNB power can be reduced up to 80% of assigned power).After attempting power scaling on the SeNB, if the total power does notexceed maximum power for the UE, the UE may transmit. Otherwise,transmission to the SeNB can be dropped (i.e., MeNB transmission may beprioritized). Instead of prioritizing on the MeNB transmission,transmission to the PCell may only be prioritized as well. In that case,the tolerance may be applied to other cells except for the PCell to meetthe maximum power. When power scaling is not feasible within thetolerance level, some channels may be dropped.

When dropping is configured, the priority of channels may be order orPRACH PUCCH-PUSCH with UCI-PUSCH without UCI-SRS. That is, the droppingpriority may be similar to scaling priority. When the same channels arecolliding with each other between two eNBs, priority eNB may beconfigured. Alternatively, order of PRACH-HARQ-ACK/SR-CSI-data may beconsidered. By default, the UE assume that higher priority is given tothe eNB which maintains C-Plane connection (e.g., PCell). By allocatingpower effectively between two eNBs and coordinating uplink subframes andscheduling, it is expected that not many subframes will experience powerlimitation case between two eNBs to avoid performance degradation ateach eNB. When two eNBs are connected by ideal or good backhaul, insteadof dropping the signals, it may be piggybacked to the other uplinksignal. From physical layer perspective, inter-site CA may be consideredas more than one higher layers are configured to the UE. Overall, thedropping or dropping rule in the power-limited case may be configured tothe UE via higher layer signaling as well. By default, the UE may assumethat power scaling rule is applied without any explicit configuration.

In the approach described above, if the allocated power to each eNB doesnot exceed the maximum power for the UE, power scaling across uplinktransmissions may not be necessary. In this case, the UE may utilizeP_(alloc) per eNB to determine which channel to protect. For example,only PUSCH transmissions are scheduled, instead of scaling down allPUSCH transmissions, at least one PUSCH transmission with power largerthan P_(alloc) per eNB may be guaranteed. Or, P_(alloc) per eNB may beused to determine which channel to drop. For example, if the powerallocated to a channel is less than P_(alloc,eNB), the channel may bedropped as it may not reach the eNB. More specifically, the value may beused for determining PUCCH drop case only.

FIG. 11 shows an example of a method for controlling uplink poweraccording to an embodiment of the present invention. The embodiment ofFIG. 11 corresponds to a method for allocating P_(alloc), which isconfigured minimum reserved power, per eNB or per carrier groupdescribed above.

In step S100, the UE allocates a first minimum reserved power for afirst carrier group and a second minimum reserved power for a secondcarrier group. The first minimum reserved power and the second minimumreserved power may be configured by the MeNB. The first minimum reservedpower and the second minimum reserved power may be configured by aratio. The first minimum reserved power and the second minimum reservedpower may not limit power of PRACH transmission of the UE. The firstcarrier group may correspond to the MeNB in dual connectivity, and thesecond carrier group may correspond to the SeNB in dual connectivity.The first carrier group may include a plurality of CCs, and the secondcarrier group may include a plurality of CCs.

In step S110, the UE applies power sharing rule for unused power exceptthe first minimum reserved power and the second minimum reserved power.The unused power may be determined as a value obtained by subtractingthe first minimum reserved power and the second minimum reserved powerfrom a maximum power for the UE. The power sharing rule may be appliedaccording to channel priority. The PRACH may have a highest priority.The PUCCH may have a higher priority than the PUSCH. The PUSCH with UCImay have a higher priority than the PUSCH without the UCI.

The UE may further perform power scaling within the first carrier groupand the second carrier group based on the first minimum reserved powerand the second minimum reserved power respectively. If there is nouplink transmission for the second carrier group, a maximum power forthe UE may be allocated to the first carrier group.

Two-step power limit according to an embodiment of the present inventionis described. In this approach, a UE is configured with maximum powerper each carrier group. First, the UE measures the total power of alluplink transmissions. To allow potentially not-aligned subframe boundaryof uplink transmissions to each carrier group, the UE may measure thetotal power at subframe n as well as n+1 (or k+1 in general). If totalpower for both subframes does not exceed the maximum power for the UE,the UE may transmit with the assigned power for each channel. If powerlimited case occurs, the UE may apply the maximum power allocated toeach carrier group per carrier group by applying the rule used in 3GPPLTE rel-11. In this case, even after power scaling, if power stillexceeds the maximum power for the UE, power scaling across eNBs may beattempted. After applying maximum power limit per carrier group, if thetotal power is less than the maximum power for the UE, unused power maybe assigned to carrier group where power scaling has occurred. If powerscaling is performed for both carrier groups, e.g., due to lower maximumpower allocated to carrier groups, then the unused power may beallocated to the MeNB or equally (or with some weights) to each carriergroup.

When determining where the total power exceeds the P_(CMAX) or not, forthe SRS, it may be measured over the symbol. However, for PUCCH orPUSCH, there could be different approaches.

The procedure of the two-step power limit is as follows.

1>If the total transmit power of the UE would not exceed, P_(CMAX)(i),transmit all channels.

1>else if P_(CMAX,eNB1)(i) and P_(CMAX,eNB2)(i) are configured withoutP_(alloc,eNB1)(i) and P_(alloc,eNB2)(i) configured:

2>if the total transmit power of the UE to eNB1 exceedsP_(CMAX,eNB1)(i), compute the unused power to the eNB2 (or other carriergroups)

3>P_(CMAX,eNB1)(i)=P_(CMAX,eNB1)(i)+unused power

3>Perform power scaling within a carrier group of the eNB1 following therule used in 3GPP LTE rel-11 to reduce the total power to the eNB1 equalor less than P_(CMAX,eNB1)(i)

2>if the total transmit power of the UE to the eNB2 exceedsP_(CMAX,eNB2)(i), compute the unused power to the eNB1 (or other carriergroups)

3>P_(CMAX,eNB2)(i)=P_(CMAX,eNB2)(i)+unused power

3>Perform power scaling within a carrier group of the eNB2 following therule used in 3GPP LTE rel-11 to reduce the total power to the eNB2 equalor less than P_(CMAX, eNB2)(i)

1>else if P_(CMAX,eNB1)(i) and P_(CMAX,eNB2)(i) are configured withP_(alloc,eNB1)(i) and/or P_(alloc,eNB2)(i) configured:

2>if the total transmit power of the UE to the eNB1 exceedsP_(CMAX,eNB1)(i), compute the unused power to the eNB2 (or other carriergroups)

3>P_(CMAX,eNB1)(i)=P_(CMAX,eNB1) (i)+unused power

3>Perform power scaling within a carrier group of the eNB1 following therule used in 3GPP LTE rel-11 to reduce the total power to the eNB1 equalor less than P_(CMAX,eNB1)(i)

2>if the total transmit power of the UE to the eNB2 exceedsP_(CMAX,eNB2)(i), compute the unused power to the eNB1 (or other carriergroups)

3>P_(CMAX,eNB2)(i)=P_(CMAX,eNB2)(i)+unused power

3>Perform power scaling within a carrier group of the eNB2 following therule used in 3GPP LTE rel-11 to reduce the total power to the eNB2 equalor less than P_(CMAX,eNB2)(i)

1>else if P_(alloc,eNB1)(i) and/or P_(alloc,eNB2)(i) are configured:

2>if the total transmit power of the UE to the eNB1 exceedsP_(alloc,eNB1)(i), compute the unused power to the eNB2 (or othercarrier groups) assuming the eNB1 is the MeMB and the MeNB isprioritized

3>P_(C,eNB1)(i)=P_(alloc,eNB1)(i)+(P_(CMAX)−P_(alloc,eNB2)(i))

3>Perform power scaling within a carrier group of the eNB1 following therule used in 3GPP LTE rel-11 to reduce the total power to the eNB1 equalor less than P_(CMAX,eNB1)(i)

2>if the total transmit power of the UE to the eNB2 exceedsP_(alloc,eNB2)(i), compute the unused power to the eNB1 (or othercarrier groups) assuming the eNB1 is the MeMB and the MeNB isprioritized

3>P_(C,eNB2)(i)=P_(alloc,eNB2)(i)+unused power

3>Perform power scaling within a carrier group of the eNB2 following therule used in 3GPP LTE rel-11 to reduce the total power to the eNB2 equalor less than P_(CMAX,eNB2)(i)

If the SeNB is prioritized, the above formulation is changed between theeNB1 and eNB2.

FIG. 12 shows an example of two-step power limit approach according toan embodiment of the present invention. Subframe #2/#3 and #6/#7 of eNB1is used for uplink transmission. At subframe #2 for the eNB0, the totalpower of the UE may not exceed the maximum power for the UE as the totalpower would be measured over subframe boundary of #2 of the eNB0 whereonly partially uplink transmission to #2 is used. Thus, even thoughinstance power at a certain point may exceed P_(CMAX), the UE may stilltransmit both uplink without any issue.

In terms of determining power limited case, a few examples may beconsidered

-   -   power limited case is determined if at any moment, maximum power        exceeds the maximum power for the UE (referring to FIG. 12,        subframe #2 of the eNB0 transmission may have power limited        case)    -   power limited case is determined if the total power over 1 ms        exceeds the maximum power for the UE (referring to FIG. 12,        subframe #2 of the eNB0 transmission may not have power limited        case)    -   power limited case is determined if one subframe overlaps with        two subframes of other carrier group transmission, and if either        one has power limited case (referring to FIG. 12, subframe #2 of        the eNB0 transmission may have power limited case)

Due to different scheduling and configuration, if network is notsynchronized, during one subframe, there may be two P_(CMAX) values. Inthis case, either the minimum or maximum value may be chosen forcomputing power limited case. Moreover, the SRS and other channel suchas PUSCH may overlap where different power limited condition may beconsidered.

In power limited case, if power limit occurs for both carrier groups,the UE may apply the maximum power allocated to each eNB individually.If power limit occurs only for single carrier group, unused power fromnon-power limited carrier group (aligned with overlapped portion) may beallocated to the other carrier group.

FIG. 13 shows another example of two-step power limit approach accordingto an embodiment of the present invention. It is assumed that atsubframe #2 of UL transmission to the eNB0 has power limited cases forthe eNB0. Unused power for the eNB1 UL can be applied to the eNB0 ULtransmission. If unused power is UPc, it may be spread over 1 ms and maybe used for power for UL transmission to the eNB0. Using the allocatedmaximum power and power added by unused portion may be used forperforming power scaling within a group again. More specifically, forPRACH power ramping, allocated power per carrier group may be used as alimit such that power ramping beyond P_(CMAX,eNB1) (or P_(CMAX,eNB2))would not be allowed. This may limit the power for PRACH, yet, it maynot cause any packet drop at physical layer.

Power limitation per carrier group according to an embodiment of thepresent invention is described. This option is similar to two-step powerlimit. Only the difference is that a UE measure the total power percarrier group. If the power exceeds the maximum allocated power for bothcarrier group, power scaling occurs within a carrier group per theallocated maximum power. If the power exceeds the maximum allocatedpower for only one carrier group, unused power from the other group isapplied to the first group and then power scaling is performed evenstill the power limited case occurs for the group. The procedure ofpower limitation per carrier group is the same as the procedure of thetwo-step power limit described above. In terms of determining “unusedpower”, a few approaches may be considered.

-   -   average of unused power over 1 ms by the other carrier group    -   minimum of unused power of n or n+1 subframe by the other        carrier group assuming subframe #n and subframe #n+1 overlap        with uplink transmission to the group    -   maximum of unused power of n or n+1 subframe    -   average of unused power of n and n+1 subframe    -   min (unused power in n subframe, P_(CMAX)−P_(alloc) _(_)        _(xeNB)) where xeNB is the eNB of subframe n.

In the description above, actual unused power may be calculatedaccording to various methods. First, if maximum power per each carriergroup is allocated, the unused power may be calculated as(P_(CMAX,eNB1)−allocated power for eNB1 carrier group). If, powerallocation ratio is configured such as 60%/40% to each eNB carriergroup, the unused power may be calculated as (P_(CMAX)*ratio toeNB1−allocated power for eNB1 carrier group). Alternatively, regardlessof power allocation, unused power may be calculated as(P_(CMAX)(i)−current power to the eNB1−current power to the eNB2).Alternatively, P_(CMAX)(i) may be chosen as a minimum betweenP_(CMAX)(i) and P_(CMAX)(i+1) where the allocated power for the eNB1 isselected as max (allocated power at subframe i, allocated power atsubframe i+1). If only the SRS is transmitted in either subframe, and ifthe SRS and other channel do not collide with each other, the power forthe SRS should not be accounted for the used power.

For P_(alloc) per eNB, P_(alloc) may be computed by configuring P_(O)_(_) _(PUSCH,c) where c is for PCell or sPCell (a cell where PUCCH istransmitted in the SeNB) and α_(c)(j) and/or Δ_(TF,c)(i)+f_(c)(i)) or asingle value may be configured. P_(O) _(_) _(PUCCH), g(i) and somemargin for PUCCH transmission may be considered. A UE may computeP_(alloc) per eNB as P_(cmin,eNBj)(i)=min {p_(CMAX,c)(j), P_(O) _(_)_(PUCCH)+PL_(c)+g(i)+Δ} or P_(cmin,eNBj)(i)=min {P_(CMAX,c)(j), P_(O)_(_) _(PUSCH)+α(j)PL_(c)+Δ_(TF,c)(i)+f_(c)(i)+Δ}. To protect PUCCHtransmission, it is desirable to use PUCCH parameters. However, the UEmay be configured with two different P_(alloc) values for PUCCH andPUSCH respectively. These values may not be applicable to PRACHtransmission. In that case, to transmit PRACH, if power scaling occurs,channel with lower power than the P_(alloc) may be dropped.Alternatively, power used for PRACH may be also used for P_(alloc) pereNB as well.

The goal of this P_(alloc) per eNB is to guarantee minimum reservedpower used for at least one uplink channel per eNB. The quality(reception quality) should be preserved so that by configuring P_(alloc)per eNB properly, and accordingly, protection of important channel suchas PUCCH or PUSCH can be achieved. For example, the MeNB may configureP_(alloc,scNB) to the minimum reserved power needed for PUCCHtransmission for the SeNB so that PUCCH transmission can be assured.Another example is to P_(alloc,MeNB) may be configured so that PUCCHtransmission to the MeNB can be assured. When P_(alloc) is configured,PRACH transmission may take higher priority such that at least one PRACHmay be transmitted regardless of P_(alloc) per eNB. In summary,P_(alloc) per eNB may be configured by higher layer or determined by theUE (and informed to each eNB optionally).

FIG. 14 shows an example of latency processing of a UE. In terms of UEprocessing latency to handle asynchronous case, depending on UEcapability, whether the UE can use both subframes to determine powerlimited case or not may be determined. For example, referring to FIG.14, the UE may need to handle power computation and resource allocationsless than 2 ms if power for subframe n and n+1 should be considered forthe other eNB's uplink transmission at subframe n. The UE may report thecapability whether it can handle the uplink grant within the shorterduration or not, so that the network may configure proper way ofhandling power limited case and computing unused power computation.Since one subframe to the eNB1 overlaps with two subframes to the eNB2,when computing unused power, two values may be computed and eitherminimum or maximum or average value may be used for lending the unusedpower to different eNB.

Assuming a network may configure different power control scheme forasynchronous case and synchronous case respectively, how to determineboth cases may be further discussed. One example is to utilize thesubframe and system frame number (SFN) offset difference between twoeNBs reported by the UE. Which mode the operation is based on may besignaled to the UE through a higher layer. Another example is based onUE capability. In this case, the UE may report which mode should beused.

UE power selection is described. Instead of network configuration, a UEmay select maximum power autonomously as well. In this case, powerheadroom report (PHR) values may be reflected properly so that each eNBcan compute the power for the UE. To address potentially TDD/FDDinter-node aggregation or TDD/TDD inter-node resource aggregation, theUE may send two sets of PHRs as well where one with high power and onewith low power depending on the uplink configuration of the other eNB.Also, the UE may send the configuration (DL/UL) and timing gap betweentwo carrier groups so that each eNB may utilize different uplinkcharacteristics.

Along with allocating maximum/minimum power per carrier group, utilizingthe maximum/minimum power only for a subset of channels instead of forall channels may be considered. For example, PRACH transmission may notbe restricted by the maximum power allocated to each group. Regardlessof the maximum power allocated to each group, PRACH may be transmittedwith highest priority with high power (yet lower than the maximum UEpower). This is to allow efficient PRACH transmission. If this case isapplied, either some channel would be dropped when PRACH is transmittedor power scaling on other channel to allow high power on PRACH may benecessary.

UE behavior to drop PRACH in a power limited case may be different ininter-node resource aggregation case and PUCCH offloading case. In PUCCHoffloading, it is up to the UE which one to drop in case of collisionwith PRACH. More specifically, in PUCCH offloading, the UE is notrequired to maintain two PRACH processes simultaneously and thuswhenever more than one PRACH collide with each other, the UE is free todrop one PRACH process. Thus, whether carrier groups are formed tosupport inter-node resource aggregation or PUCCH offloading may beassumed. It may be further assumed that the UE is not configured withboth inter-node resource aggregation and PUCCH offloading case unlessPUCCH carrier is shared between two eNBs by some means.

Additionally, when a UE performs power scaling and inter-site CA isconfigured, the UE may indicate that power scaling is applied.Alternatively, the UE may indicate that power scaling is used regardlessof inter-site or intra-site CA. A multiple approach may be feasible toinform whether the power scaling has been applied or not. One example isto change demodulation reference signal (DMRS) sequence of PUSCH byusing different initialization value or cyclic shift. For example,

$c_{init} = {{\left\lfloor \frac{N_{ID}^{cell}}{30} \right\rfloor \cdot 2^{10}} + f_{ss}^{PUSCH}}$

may be configured for PUSCH which has been power-scaled. Other means todifferentiate DMRS sequence between PUSCH with/without power scaling maybe used. Another example is to transmit the information through higherlayer so that higher layer may report power limitation occurrence. Inthis case, power scaling report may be reported to both eNBs (i.e., morethan one higher layers) when dual connectivity is configured for theMeNB and SeNB.

Furthermore, if it is assumed that a UE is able to indicate whetherpower scaling is used or not, different modulation and coding scheme(MCS) may be considered with and without power scaling on PUSCHtransmission. For example, if MCS=8 has been configured to a UE withconfigured power, then MCS=6 may be used when power scaling is applied.A set of mapping table between MCS delta and power scaling amount may beconsidered as well. For example, MCS delta may be 2 when power scalingis 2 dB.

If P_(alloc) is configured per each carrier group or per eNB where a UEreserves the allocated power to the other eNB, then there may be poweravailable even though the UE has only SRS transmission scheduled. If therequested power for SRS is higher than P_(alloc,xeNB), then there aretwo choices. First is dropping the SRS as power is not sufficient, andsecond is transmitting the SRS with remaining power. When determiningwhether to use remaining power for SRS transmission or not, the UE maylook-ahead for transmissions to the other eNB so that it uses power onlywhen the other eNB or carrier group does not have any data (other thanSRS). If remaining power is not available due to potential transmissionin the other eNB or power limited case, since at least P_(alloc) isreserved, it may be further considered to transmit SRS with lower powerthan the requested. In this case, it is desirable to notify that SRS hasbeen transmitted with lower power (P_(alloc)) by using differentscrambling sequence or other means. Some remaining power may be appliedeven though it still not meet the requested power for the SRS. It is notdesirable to transmit SRS with the remaining power. Thus, it may beassumed that if the SRS is transmitted, the power may be either (1)P_(CMAX), (2) P_(alloc,xeNB) (3) the requested power.

Not to disturb power control loop, it may be assumed that the SRS isdropped if (1) or (3) cannot be met (i.e., either P_(CMAX,c) or therequested power). In other words, the SRS may be transmitted only if therequested power for the SRS has been satisfied or P_(CMAX,c) has beenreached.

FIG. 15 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

An eNB 800 may include a processor 810, a memory 820 and a radiofrequency (RF) unit 830. The processor 810 may be configured toimplement proposed functions, procedures and/or methods described inthis description. Layers of the radio interface protocol may beimplemented in the processor 810. The memory 820 is operatively coupledwith the processor 810 and stores a variety of information to operatethe processor 810. The RF unit 830 is operatively coupled with theprocessor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The RF unit 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

1-14. (canceled)
 15. A method for controlling, by a user equipment (UE),an uplink power for dual connectivity in a wireless communicationsystem, wherein the UE is connected to both a master cell group (MCG)and a secondary cell group (SCG) in the dual connectivity, the methodcomprising: receiving, by the UE, a first configuration of a firstmaximum power for the MCG and a second configuration of a second maximumpower for the SCG; determining, by the UE, that a sum of a firsttransmission power for the MCG and a second transmission power for theSCG exceeds UE maximum power, wherein the first transmission power isdetermined based on the first maximum power and the second transmissionpower is determined based on the second maximum power; reducing, by theUE, the second transmission power so that a sum of the firsttransmission power and the reduced second transmission power does notexceed the UE maximum power.
 16. The method of claim 15, wherein thefirst configuration is received from a first network node serving theMCG, and wherein the second configuration is received from a secondnetwork node, different than the first network node, serving the SCG.17. The method of claim 15, wherein the MCG belongs to a first radioaccess technology (RAT), and wherein the SCG belongs to a second RAT.18. The method of claim 15, wherein a subframe boundary of the MCG and atime duration boundary of the SCG is not aligned with each other. 19.The method of claim 18, wherein the sum of the first transmission powerand the second transmission power exceeds the UE maximum power isdetermined at a specific time duration of the SCG, which is overlappedwith subframes n and n+1 of the MCG.
 20. The method of claim 15, furthercomprising performing power scaling across component carriers (CCs)which belong to each of the MCG and the SCG respectively, based on achannel priority.
 21. The method of claim 20, wherein an order of thechannel priority is a physical random access channel (PRACH), a physicaluplink control channel (PUCCH), and a physical uplink shared channel(PUSCH) with uplink control information (UCI), a PUSCH without UCI, anda sounding reference signal (SRS).
 22. A user equipment (UE) in awireless communication system, wherein the UE is connected to both amaster cell group (MCG) and a secondary cell group (SCG) in the dualconnectivity, the method comprising: a memory; a radio frequency (RF)unit; and a processor, operably coupled to the memory and the RF unit,that: controls the RF unit to receive a first configuration of a firstmaximum power for the MCG and a second configuration of a second maximumpower for the SCG; determines that a sum of a first transmission powerfor the MCG and a second transmission power for the SCG exceeds UEmaximum power, wherein the first transmission power is determined basedon the first maximum power and the second transmission power isdetermined based on the second maximum power; reduces the secondtransmission power so that a sum of the first transmission power and thereduced second transmission power does not exceed the UE maximum power.23. The UE of claim 22, wherein the first configuration is received froma first network node serving the MCG, and wherein the secondconfiguration is received from a second network node, different than thefirst network node, serving the SCG.
 24. The UE of claim 22, wherein theMCG belongs to a first radio access technology (RAT), and wherein theSCG belongs to a second RAT.
 25. The UE of claim 22, wherein a subframeboundary of the MCG and a time duration boundary of the SCG is notaligned with each other.
 26. The UE of claim 25, wherein the sum of thefirst transmission power and the second transmission power exceeds theUE maximum power is determined at a specific time duration of the SCG,which is overlapped with subframes n and n+1 of the MCG.
 27. The UE ofclaim 22, wherein the processor further performs power scaling acrosscomponent carriers (CCs) which belong to each of the MCG and the SCGrespectively, based on a channel priority.
 28. The UE of claim 27,wherein an order of the channel priority is a physical random accesschannel (PRACH), a physical uplink control channel (PUCCH), and aphysical uplink shared channel (PUSCH) with uplink control information(UCI), a PUSCH without UCI, and a sounding reference signal (SRS).